1. Field of Invention
The present invention relates to a method for reducing scalp staining when metal ion pretreatments are used to activate dyeing processes on live heads.
2. Description of the Prior Art
The use of metal ion treatments to activate a variety of hair coloring processes is know in the art. For example Ger. 2,028,818 discloses accelerated oxidative dyeing by use of a pretreatment containing one of a variety of metal ions. Autooxidative dyeing systems which usually contain dye ingredients, such as pyrogallol, 1,2,-4-trihydroxybenzene or other readily oxidized phenolics, are also claimed to be activated by metal ions (see for example U.S. Pat. No. 629,231).
Natural dyes and natural dye precursors that are known in the art as being capable of being activated by metal ions, include: indolic compounds (U.S. Pat. Nos. 2,934,296, and 3,194,734 and GB 797,174), logwood extracts (U.S. Pat. No. 4,801,302), henna and other quinone dyes (Czech 142,851).
Commercial exploitation of such dyeing processes is severely restricted by the fact that they have a number of significant drawbacks. The foremost drawback is the unacceptable amount of scalp staining produced when these dyeing systems are used on live heads. The affinity of metal ions for hair keratin and skin is quite similar. Therefore, a significant fraction of the metal ion applied is adsorbed by the scalp skin. Metal ion adsorbed by skin and metal adsorbed by hair have equivalent reactivity in the dyeing processes. Thus, a significant amount of color is produced on the scalp during hair dyeing. This is undesirable. With permanent dyes, i.e. dyes that are not readily removed by shampooing, the scalp coloration that is produced can last for a considerable time. Thus prior art processes are unsatisfactory.
The present invention provides an improvement in a process for dyeing hair on a live head wherein the hair is treated with metal ion in a pretreatment step to accelerate subsequent dyeing of the hair and the treated hair is then subjected to an oxidative or autooxidative dyeing step. The improvement comprises,
(a) between the pretreatment step and the dyeing step the scalp of said live head is subjected to vigorous massage, rubbing, combing or brushing, for a time sufficient to reduce staining of the scalp occasioned by the dyeing step; or
(b) sufficient time is permitted to elapse between the pretreatment step and the dyeing step to reduce staining of the scalp occasioned by the dyeing step; or
(c) between the pretreatment step and he dyeing step the scalp of said live head is subjected to vigorous massage, rubbing, combing or brushing and time is permitted to elapse between the pretreatment step and the dyeing step, the duration of the massage rubbing, combing or brushing coupled with the duration of the elapsed time between the pretreatment and dyeing steps being sufficient to reduce staining of the scalp occasioned by the dyeing step.